Dermatology Flashcards
Approach to cases, revision, diagnostic sampling
What are the functions of the skin?
- Protection
- Production of glandular secretions
- Sensory
- Storage (fat)
- Thermoregulation
- Communication
What is the most common skin bacterial pathogen in the dog?
Staphylococcus pseudintermedius
What is the periople?
The band of soft rubbery horn over the perioplic dermis of the hoof, proximal to the coronary dermis
What points need to be established before treatment for a dermatological condition can be started?
- What is happening to the skin
- Why this is happening, often secondary to a primary underlying cause (dermatological or systemic)
List the main diagnostic tests used when working up a dermatology case
- Coat brushings
- Skin scrapes
- Skin cytology
- Dermatophyte culture
- Trichograms
- Wood’s lamp examination
What tests may be required if the basic investigation of a dermatological disease does not give a diagnosis?
- Blood tests
- Skin biopsies
- Microbial culture
What dermatological conditions are more likely in <1yo animals?
- Immunologial immaturity
- Demodicosis
- Dermatophytosis
- Juvenile pyoderma
- Congenital defects
What dermatological conditions are more likely in <3yo animals?
- Atopy
- Follicular dyspasia
- Keratinisation defects
- Histiocytomas
What dermatological conditions are more likely in >6yo animals?
- Hypothyroidism
- Hyperadrenocorticism
- Neoplasia
In an entire male with endocrine or dermatological changes, what is a key differential?
Testicular neoplasia producing/altering hormone production
What information do you need to know when working up a dermatology case?
- When condition started
- Details of in contact animals
- lesions on people
- How long owned
- Housing and management
- Travelled abroad
- Past derm. history
- Treatments given and response
- Flea control
- Exposure to potential sources of infection
What should be investigated in a clinical exam in the work up of a dermatology case?
- Full clinical exam
- Signs of systemic disease that may: underlie derm disease, affect diagnostic approach, affect treatment of skin
- Signs associated with derm. disease e.g. lymphadenopathy with demodicosis, severe inflammation or lymphadenopathy from metastasis of skin neoplasm
Describe the dermatological examination when working up a dermatology case
- Thorough and systematic: ears, interdigital spaces, claws, footpads, MMs,
- Need good lighting and adequate restraint (sedation?) clip hair
- Identify and record lesions and lesion groupings
What are the most common causes of dermatological disease?
- Metabolic (incl. endocrine)
- Neoplastic
- Inflammatory
- Immune mediated: hypersensitivities, auto-immune
- Infectious: parasitic, bacterial, fungal, protozoal, viral
- Traumatic
In what situations would you use unstained or stained acetate tape strips?
- Stained: bacteria, yeasts, cytology
- Unstained: parasites e.g. surface mites
What are the advantages of in house tests for dermatology cases?
- Rapid results while owner in practice
- Provide diagnosis or rule out differentials
- Specific and appropriate treatment can be prescribed
- Reduce risk of unnecessary symptomatic treatment
- Improved monitoring of the response to treatment
- Cost effective to perform and improves practice income
What microscope objectives are best used for ectoparasites and hairs?
x4 and x10 objectives
What microscope objectives are best used for bacteria and yeasts, inflammatory and tissue cells?
x100 objective (oil)
What diagnostic tests are best for parasites?
- Coat brushings
- Coat combings (surface mites)
- Acetate tape (unstained)
- Skin scrapings (deep for Demodex, superficial for surface mites)
- Plucks (demodicosis)
- Biopsy
- Examination of ear wax in liquid paraffin (Otodectes)
What diagnostic tests are best used for microbes?
- Cytology (esp. bacteria and yeasts)
- Bacterial culture: surface, fresh pustule, tissue biopsy optimal
- Fungal culture (from hair plucks from lesion periphery, or McKenzie coat brushing)
- Hair plucks examined under light microscope for dermatophytosis
- Wood’s lamp for dermatophytosis
Outline the value of hair as a diagnostic sample for dermatological disease
- Trichograms
- pluck with haemostats, lie on liquid paraffin under coverslip
- Also differentiation between alopecia as primary disease process, or due to self trauma
- Self trauma indicated by broken distal tips
Describe the appearance of hair shafts affected by dermatophytosis
Covered with spores and penetrated by hyphae
What is the result of melanin clumping in hair?
Colour dilution alopecia
Outline the assessment of the hair bulb in a dermatology case
- Assess to establish stage of hair growth
- Telogen: hairs pear shaped, rough and non-pigmented, usually 80-90% of hairs, inactive and all hairs in telogen is suggestive of endocrinopathy
- Anagen: bulbs rounded, smooth +/- pigmented centre, bulb may fold around shaft when plucked, actively growing hairs, normally 10-20% (poodles have more)
When should cytology be carried out with regards to dermatology cases?
In all dermatology cases
Give examples of cytology samples used in dermatology
- Impression smears (erosions, ulcers, exudate, pustules, papules, indirect from biopsy)
- Tape strips (crusts, scaling, alopecia, lichenification, erythematous skin)
- Swab smears (transfer from swab to slide by rolling along surface)
- FNA
- Staining with DiffQuik
When should superficial skin scrapes be carried out?
All pruritic animals and scaling dermatosis
How many samples should be taken when performing skin scrapes?
3-5 sites should be scraped
What can be found on superficial skin scrapes?
- Cheyletiella (usually dorsal aspect with scaling)
- Notoedres cati
- Otodectes cynotis usually preauricular skin, head, neck, tail base)
- Trombicula autumnalis
- Dermatophyte spores
When should deep skin scrapes be carried out?
- In all cases of alopecia +/- pruritus
- All cases of greasy skin
- Comedones
- crusting
- Papules
- Pustules
What can be found on deep skin scrapings?
- Demodex
- Sarcoptes scabiei
Where and how many deep skin scrapes should be taken?
- 3-5 sites
- Demodex: edges of alopecic skin, comedones, erythema, papules, pustules, crusts, need to squeeze skin before scraping
- Sarcoptes: ear margins, elbows, hocks, ventral abdomen, papules, crusted papules, untraumatised skin
What should you do if you are suspicious of Sarcoptes, but nothing is found on deep skin scrapings?
Prescribe 6-week diagnostic therapeutic trial, using selamectin or sarolaner
Explain the steps required in allergy workups
1: Rule out secondary infections and ectoparasites using other techniques
2: Rule in or out FAD, ultimate diagnosis depends on response to treatment
3: Rule in or out adverse food reaction by response to food trial and confirmation by challenging with suspected food
4: Clinical diagnosis of atopic dermatitis based on Favrot’s criteria, diagnosis of exclusion
- Serum and or intradermal allergy testing only following clinical diagnosis of atopic dermatitis once other causes of pruritus have been excluded
How many of Favrot’s criteria must be fulfilled to be diagnosed with atopic dermatitis?
5 of 8 need to be present
List Favrot’s criteria
- Age of onset <3yo
- Dog mostly indoors
- Corticosteroid responsive
- Chronic or recurrent yeast infection
- Affected feet
- Affected ear pinnae
- Non-affected ear margins
- Non-affected lumbosacral area
What actions should be taken if bacteria are found on cytology?
- If coccid: treat or culture if chronic/recurrent
- If rods: always culture
What actions should be taken if Malassezia are found on cytology?
Treat (e.g. shampoos, anti-fungal treatment)
What actions should be taken if fungal hyphae and spores are found on cytology?
Culture
What actions should be taken if macrophages are found on cytology?
Culture and/or biopsy
What actions should be taken if round cells are found on cytology?
a: lymphocytes
b: histiocytes
c: mast cells
a: biopsy
b: possible histiocytoma, histopathology or could wait and see
c: excisional biopsy and histopathology
When should skin biopsies be used?
- To establish definitive diagnosis that cannot be reached by other, less invasive methods
- Suspected neoplasm
- Persistent ulceration/vesicular lesions
- Skin disease unresponsive to rational treatment
- Unusual or apparently serious disease, esp/ if animal unwell
- Before using dangerous/expensive drugs
- To rule out certain conditions
What types of lesions are ideal for skin biopsy?
- Early in disease to minimise chronic changes
- Primary lesion, mature lesion, multiple biopsies covering a range of lesions
How should a skin biopsy for alopecia be taken?
Include normal skin and mark direction hair growth (wedge biopsy)
How should a skin biopsy for ulcerated lesions be taken?
Include margin or normal and ulcerated skin (wedge biopsy)
What are the basic structures in the skin?
- Epidermis
- Dermis
What are the layers in the epidermis, and in which order are they formed?
Starting at the deepest layer:
- Stratum basale
- Straum spinosum
- Stratum granulosum
- Stratum corneum
Describe the changes that occur in keratinocytes as they move towards the surface
More keratin, polyhedral, become flattened and anuclear
How are epidermal cells joined to each other?
- Desmosomes and hemidesmosomes, tight junctions
- Desmosomes: cell to cell
- Hemidesmosomes: cell to protein
- Tight junctions cell to cell
What is the difference between a papule and a nodule?
- papule is a small pimple/swelling on skin, often part of a rah, <1cm diameter
- Nodule is small swelling or aggregation of cells in the body, esp. an abnormal one, >1cm diameter
What is the difference between a macule and a patch?
- Macule is an area of skin discolouration <1cm diameter
- Patch is a flat circumscribed area of discolouration >1cm,
What is the difference between a vesicle and a bulla?
- Vesicle is a small circumscribed elevation of epidermis containing clear fluid <1cm
- Bulla is a large blister with serous fluid, >1cm diameter
What is the difference between an erosion and an ulcer?
- erosion is discontinnuty of the skin, exhibiting incomplete loss of epidermis, usually most, circumscribed and depressed
- Ulcer is a sore on skin or a MM, accompanied by disintegration of tissue
What is the difference between scale and crust?
- Scale is the accumulation of loose fragments of the stratum corneum
- Crust is a secondary lesion of dried exudate/serum/blood/medication/excessive scale on skin surface, or sequel to a pustule
What is the difference between acanthosis and hyperkeratosis?
- Acanthosis is diffuse epidermal hyperplasia, increased depth of epidermis, more layers
- Hyperkeratosis is abnormal thickening of outer layer of skin, increased depth of cornified layer, more layers
Name the major myiasis flies
- Oestridae (bot and warble)
- Sarcophagidae (flesh flies)
- caliphoridae (blow, bottle flies)
- Muscidae (some house flies)
Name the major nuisance flies
- House (Musca domestica and autumnalis)
- Head flies (Hydrotaea irritans)
- Stable flies (Stomoxys calcitrans)
- Horn flies (Haematobia irritans)
Name the dog lice and identify as chewing or sucking
- Trichodected: chewing
- Linognathus: sucking
Name the cat louse and identify as chewing or sucking
Felicola, chewing
Name the horse lice and identify as chewing or sucking
- Damalinia: chewing
- Haematopinus: sucking
Name the cow lice and identify as chewing or sucking
- Damalinia: chewing
- Haematopinus, Linognathus: sucking
Name the sheep and goat lice and identify as chewing or sucking
- Damalinia: chewing
- Linognathus: sucking
Name the pig louse and identify as chewing or sucking
Haematopinus suis: sucking
Name the poultry lice and identify as chewing or sucking
- Lipeurus
- Cuclogaster
- Menacanthus
- All chewing
Name the guinea pig lice and identify as chewing or sucking
- Gliricola
- Gyropus
- Both chewing
Name the dog surface mites
- Cheletiella yasurgi
- Otodectes cynotis
- Trombicula autumnalis
Name the dog deep mites
- Sarcoptes scabiei
- Demodex
Name the cat surface mites
- Cheyletiella blakei
- Otodectes cynotis
- Trombicula autumnalis
Name the cat deep mite
Notoedres cati
Name the horse surface mites
- Psoroptes equi
- Chorioptes bovis
Name the horse, cow, sheep and pig deep mite
Sarcoptes
Name the cow surface mites
- Psoroptes ovis
- Chorioptes bovis
Name the sheep surface mite
Psoroptes ovis
Name the pig surface mite
Psoroptes suis
Name the poultry surface mites
- Dermanyssus
- Ornithonyssus
Name the poultry deep mite
Knemidocoptes
Name the rabbit surface mites
- Cheyletiella parasitivorax
- Psoroptes cuniculi
- Listrophorus
Name the guinea pig surface mite
Chirodiscoides
Name the guinea pig deep mite
Trixicarus cavidae
Compare the appearance of Ixodes, Dermacentor and Rhipicephalus ticks
- Ixodes: large mouthparts, inornate, no festoons, anal groove in front of anus
- Dermacentor: eyes present, palpi wider than long, ornate, festoones, basis capituli rectangular, anal groove below anus and U shaped
- Rhipicephalus: eyes present, palpi wider than long, inornate, festoons, basis capituli hexagonal, anal groove below anus and wine glass shaped
Give examples, activity against G+ve and G-ve, pseudomonas, and whether bacteriostatic or bactericidal for beta-lactam antibiotics
- Amoxicillin clavulanate, cephalezin, cefoveci
- Active against G+ve and -ve
- No activity against Pseudomonas
- Bactericidal
Give an example, activity against G+ve and G-ve, pseudomonas, and whether bacteriostatic or bactericidal for macrolide antibiotics
- Clindamycin
- Active against G+ve, G-ve intrinsic resistance
- No acitivyt against Pseudomonas
- Bacteristatic
Give examples, activity against G+ve and G-ve, pseudomonas, and whether bacteriostatic or bactericidal for potentiated sulphonamide antibiotics
- TMPS
- Active against G+ve and -ve
- No activity against Pseudomonas
- Bactericidal
Give examples, activity against G+ve and G-ve, pseudomonas, and whether bacteriostatic or bactericidal for fluroquinolone antibiotics
- Enrofloxacin, marbofloxacin, pradofloxacin, orbifloxacin
- Active against G+ve and G-ve
- Active against Pseudomonas
- Bacteristatic
Give examples, activity against G+ve and G-ve, pseudomonas, and whether bacteriostatic or bactericidal for aminoglycoside antibiotics
- Gentamycin, framycetin, fusidic acid, polymixinB
- Active against G+ve: only framycetin and fusidic acid
- Active againse G-ve: only gentamycin, framycetin, polymixin B
- Active against Pseudomonas: genta fram, polymixin B
- All but fusidic acid are bactericidal
Key points on type I hypersensitivities
- Rapid, 15-20 mins
- Sensitised individuals
- Mast cell bound IgE cross links, degranulate, release of bioactive molecules
- Oedema, inflammation, bronchoconstriction, pruritus
Key points on type II hypersentivities
- Target cell destroyed by binding of IgG or IgM to cell surface antigen
- Cytolysis due to complement or NK cells or target phagocytosed by macrophage
- Ab recognises self antigen on host or tissue cell, or Ab recognises small molecuels attached to cell or tissue
- E.g. thrombocytopaenia, haemolytica anaemia, myasthenia gravis
Key points on type III hypersensitivity
- Reaction ~4-8hrs
- Immune complex mediated
- Deposition of Ab/Ag complexes in vessels or tissues, escape normal clearance
- Ab or Ag excess
- Ag soluble, endo or exogenous source
- Localised reaction = Arthus reaction
- Allergy to fugal spores in cattle, recurret airway obstruction in horses, blue eye and Leishmaniasis in dogs
- Also SLE, polyarthritis, nephritis
Key points on type IV hypersensitivities
- Delayed type, within 24-72 hours
- T cell mediated, interaction between dendritic and primed T cells
- T recognise Ag, recruit and activate mononuclear cells via IFNy and chemokines
- HEvs form, upregulation of vascular adressins
- Inflammation at site of interaction
- Tuberculin reaction in skin, granuloma formation e.g. pemphigus foliaceous
Explain the significance of finding bacilli on cytology for a dermatology case
- Unless suspect faecal contamination, need to carry out bacterial culture and sensitivity where possible
- May indicate Pseudomonas, which are frequently resistant to antibiotics
Describe the appearance of degenerating neutrophils
- Nuclei lose lobulaion
- Nuclei swell
What is indicated by a cytology sample with;
a: >70% granulocytes present?
b: >50% monocytes present?
c: mixture of neutrophils and macrophages?
a: Acute inflammation
b: chronic inflammation
c: pyogranulomatous inflammation
What is required in order to confirm whether a pustule/inflammatory lesion is truly sterile?
Must carry out culture - easy to get false negatives, esp. with pyogranulomatous inflammation
What does finding nucleated keratinocytes on cytology indicate?
- Can indicate more rapid epidermal turnover e.g. inflammation
- Also a specifi c feature of certain diseases causing parakeratotic hyperkeratosis (e.g. zinc deficiency, hepatocutaneous syndrome)
Describe the appearance of epithelial granules
- Within epithelial cells only
- tend to stain lighter/brown vs basophilic bacteria
What causes the appearance of nuclear chromatin streaks?
From ruptured cells
What information can be gained from Trichograms?
- Presence of Demodex, lice, Cheyletiella eggs
- Presence of dermatophytes on shaft (low sensitivity)
- Anagen/telogen bulbs, shaft/tip abnormalities
Explain why skin biopsy is particularly useful in Shar Peis
Skin may be too thick and lead to false negatives on skin scrapes, so biopsy may be needed for detection of demodicosis
Outline the requirements for skin biopsy
- Sample representative of lesion
- Multiple samples if possible (min. 3)
- Sample fully developed lesions where possible
- Alopecia: biopsy max hair loss, margin to normal and normal haired skin
- Ulcerated: ulcerated area and area just adjacent, where epidermis still in tact
- Pustules, vesicles, bullae: remove whole lesion without disruption
State whether incisional or excisional biopsy would be most appropriate for the following lesions:
a: excision of soitary nodule
b: vesicles
c: transition between normal and lesional skin e.g. alopecia, ulceration edges
d: biopsy of cutaneous masses
e: suspected deep lesions e.g. panniculitis
a: Excisional
b: Excisional (less likely to damage than a punch)
c: Incisional
d: Incisional
e: Incisional
